Electric power generating element

ABSTRACT

In an electric power generating element, either positive or negative electrode includes a composition containing an organic compound as a main agent and the positive electrode has an electrically conductive substance so that relatively low-temperature thermal energy is efficiently converted to electric energy. Polyethylene glycol is employed as the organic compound and graphite or a graphite composition is employed as the conductive substance. Salt providing ionic conductivity may be added to the organic compound or polyethylene glycol, and the negative electrode may be formed of a metal having an ionization tendency as large as or larger than copper or a composition of the metal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an electric power generating element capableof efficiently converting a low-temperature heat energy to an electricenergy.

2. Description of the Prior Art

Demands for diversification of energy resources, global environmentprotection and so on have proposed applications of thermoelectricgeneration of electricity employing a thermoelectric generating elementby use of the Seebeck effect to a small-scale power generation. Forexample, a fossil fuel such as propane is burned by means of a burnerand then, a heat source with a capacity up to 820 K obtained from theburning of the fossil fuel is applied to a thermoelectric generatingelement composed of the system of PbTe so that thermo-electromotiveforce is generated by the Seebeck effect. In another proposed method,the fossil fuel is gradually burned in the presence of a platinumcatalyst such that a heat source with a capacity up to 600 K isobtained. The heat source is applied to a thermoelectric generatingelement composed of the system of BiTe. In further another proposedmethod, a nuclear reactor or radioactive elements are used as the heatsource to apply heat to a thermoelectric generating element composed ofthe system of SiGe when the supply of the fossil fuel is difficult.

However, a high-temperature heat source is required in theabove-described conventional methods of the thermoelectric generation ofelectricity, resulting in a low efficiency of thermoelectric conversion.Further, the fossil fuel, the nuclear reactor or the radioactive elementis required to obtain the high-temperature heat source and accordingly,a large-scale apparatus for the thermoelectric generation isnecessitated. Thus, the conventionally proposed methods ofthermoelectric generation are contrary to demands for compactness andcost effectiveness. Further, the running cost would become high and asufficient energy saving effect would not be expected.

The prior art also provides as another related art a solar batterywherein solar energy is converted to electric energy by the photovoltaiceffect. The solar battery is expensive and cannot be used when thesunlight is not available. Further, the solar battery has a criticaldefect that the heat energy other than light energy cannot be convertedto the electric energy. Additionally, the solar battery requires a largespace for receiving the sunlight, which is contrary to the demands forcompactness and cost effectiveness.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide an electricpower generating element wherein low-temperature heat energy such asexhaust heat can be used as a heat source and the low-temperature heatenergy can be efficiently converted to the electric energy so that aneconomic power generation can be provided, sufficient energy saving canbe achieved and the element can contribute to the global environmentprotection, and wherein the compactness and cost effectiveness of theelement can also be achieved.

The inventor of the present invention has been engaging in the study ofthe system of polyethylene glycol-graphite serving as a positiveself-temperature control plane heating element, and has been granted aJapanese patent No. 1,647,696 (Japanese Published Patent Application No.3-10203). The polyethylene glycol-graphite system will be referred to as"PG-GC system" hereafter. Subsequently, the inventor succeeded inexplicating the switching and the relationship between current andvoltage in the PG-GC system on the assumption of occurrence of theelectron transfer from the graphite to the polyethylene glycol in theprocess of elucidating an electrically conducting mechanism of the PG-GCsystem. Consequently, the inventor had a conception that the PG-GCsystem would function as an electric power generating element. Afterexperiments, the inventor made an invention of an electric powergeneration element generating an electromotive force and a short-circuitcurrent whose values were larger than expected.

The present invention provides an electric power generating elementconverting a low-temperature heat energy to an electric energy,comprising a positive electrode containing graphite a negative electrodeformed from a metal, and at least polyethylene glycol which can exist asa solid or liquid. At least one of the electrodes contacting the atleast one glycolic organic substance. The electron transfer from thegraphite to the polyethylene glycol can be conceived as a reaction atthe side of the positive electrode in the electric power generatingelement:

    GC+PG→GC.sup.+ +PG (et.sup.-)

where PG is polyethylene glycol and GC is graphite. The experimentalresults show the movement of electric charges to the polyethylene glycolthough this reaction has not conventionally been known in the art.

As to the reaction at the side of the negative electrode, copper ionswere recognized to be in a solution of lithium chloride-polyethyleneglycol as the result of an inductively coupled plasma emissionspectrometry. In this case, lithium chloride was employed for providingthe ionic conductivity. Consequently, copper leaves the electrons in theelectrode at the negative electrode side, dissolving out as positiveions into polyethylene glycol:

    Cu→Cu.sup.++ (or Cu.sup.+)+e.sup.- (within electrode).

It is considered that in this reaction, an external current flows sincethe electrons left in the copper electrode flows through an externalcircuit, reaching the positive electrode to transfer into polyethyleneglycol. It has not conventionally been considered that copper dissolvesout into polyethylene glycol. In the present invention, the reason forthe solution of copper into polyethylene glycol would be that copperwould be stable when it is coordinated as ions with polyethylene glycolor that copper could dissolve out easily by the effect of potentialinduced by transfer of electrons at the positive electrode.

At first, the inventor considered that products of thermal decompositionof polyethylene glycol, for example, carbonyl such as aldehyde orketone, acidifies the copper electrode such that the copper ionsdissolve out. However, as will be described in a first embodiment of thepresent invention later, polyethylene glycol after discharge wasmeasured by way of the infrared spectroscopic analysis and the resultwas compared with that of unused polyethylene glycol. Consequently, nodifference was found between the spectrum of polyethylene glycol afterdischarge and that of the unused polyethylene glycol, and no products ofthe thermal decomposition such as aldehyde or ketone could be found.

Also as will be described in the first embodiment, lithium chloride,sodium chloride and potassium chloride were added to polyethylene glycolrespectively so that these solutions take an approximately equal molarconcentration. Then, when electromotive forces and short-circuitcurrents in these solutions were compared with one another, almost nodifference could be seen among the electromotive forces andshort-circuit currents in the three salt systems. Consequently, it canbe considered that the salt plays only a part to increase theconductivity of the system. Accordingly, any kind of salt can beemployed regardless of an organic and inorganic acid salt, only if itcan provide the conductivity. However, any kind of salt with a largersolubility is preferable.

In consideration of the facts as far as described above, the electricpower generating element of the present invention basically comprises anorganic compound (polyethylene glycol) and an electrically conductivesubstance (graphite). Any kind of salt may be employed as an electrolyteonly if it can provide the system with the conductivity. A positiveelectrode includes a conductive material which is graphite or acomposition of graphite and a negative electrode is formed of a metalhaving an ionization tendency same as or larger than copper or acomposition of the metal.

Furthermore, when a separator is interposed between the positive andnegative electrodes, contact between the electrodes can be prevented bythe separator in case that the electric power generating element isthinned.

When an activator such as manganese dioxide is added to the compositionat the side of the positive electrode, electrode reaction can beefficiently performed.

When the negative electrode is formed of a metal having a highionization tendency, the electromotive force can be efficientlyincreased.

Furthermore, when two sheets of a nonwoven fabric are impregnated withthe compositions of the electrodes respectively, the thickness of theelectric power generating element can be reduced and the short-circuitcurrent can be increased with reduction of the inner resistance.Additionally, when the nonwoven fabric is formed of a synthetic resinsuch as a polyester resin, each composition does not permeate thenonwoven fabric. Consequently, the density of the components of eachcomposition can be prevented from being varied because of thepermeation.

Other objects of the present invention will become obvious uponunderstanding of the illustrated embodiments about to be described.Various advantages not referred to herein will occur to those skilled inthe art upon employment of the invention in practice.

BRIEF DESCRIPTION OF THE DRAWINGS

Several embodiments of the present invention will be described withreference to the accompanying drawings in which:

FIG. 1 is a sectional view of the electric power generating element of afirst embodiment of the present invention;

FIG. 2 is a graph showing the relationship between the electromotiveforce of the element and the temperature;

FIG. 3 is a graph showing the relationship between the short-circuitcurrent between the electrodes and the temperature;

FIG. 4 is a longitudinally sectional front view of the liquid phaseelectric power generating element employed in the experiment;

FIG. 5 is a longitudinally sectional side view of the liquid phaseelectric power generating element;

FIG. 6 is a graph showing the relationship between the short-circuitcurrent and the temperature in the liquid phase electric powergenerating element comprising the system of lithiumchloride-polyethylene glycol (#300), a positive electrode formed of agraphite plate and a negative electrode formed of a copper plate;

FIG. 7 is a graph showing the relationship between the electromotiveforces and the temperatures in the liquid phase electric powergenerating elements wherein three systems of lithium chloride, sodiumchloride and potassium chloride having approximately equal molarconcentration are added to polyethylene glycol (#300) respectively andeach of which having a positive electrode formed of a graphite plate anda negative electrode formed of a copper plate;

FIG. 8 is a graph showing the relationship between the short-circuitcurrents and the temperatures in the liquid phase electric powergenerating elements wherein three systems of lithium chloride, sodiumchloride and potassium chloride having approximately equal molarconcentration are added to polyethylene glycol (#300) respectively andeach of which having a positive electrode formed of a graphite plate anda negative electrode formed of a copper plate;

FIG. 9 is a graph showing the relationship between the short-circuitcurrent and the elapsed time period in the liquid phase electric powergenerating element comprising the system of one weight percentage oflithium chloride-polyethylene glycol (#300), a positive electrode formedof a graphite plate and a negative electrode formed of a copper plate;

FIG. 10 is a sectional view of the electric power generating element ofsecond through fifth embodiments of the invention;

FIG. 11 is a graph showing the relationship between the electromotiveforce and the temperature in the element and the relationship betweenthe short-circuit current density and the temperature in the element ofthe second embodiment;

FIG. 12 is a graph showing the relationship between the electromotiveforce and the temperature in the element and the relationship betweenthe short-circuit current density and the temperature in the element ofthe third embodiment;

FIG. 13 is a graph showing the relationship between the electromotiveforce and the temperature in the element and the relationship betweenthe short-circuit current density and the temperature in the element ofthe fourth embodiment;

FIG. 14 is a graph showing the relationship between the electromotiveforce and the temperature in the element and the relationship betweenthe short-circuit current density and the temperature in the element ofthe fifth embodiment;

FIG. 15 is a graph showing the relationship between the electromotiveforce and the temperature in the element of the sixth embodiment;

FIG. 16 is a graph showing the relationship between the short-circuitcurrent between the electrodes and the temperature in the sixthembodiment;

FIG. 17 is a graph showing the relationship between the electromotiveforce and the temperature in the element of the seventh embodiment;

FIG. 18 is a graph showing the relationship between the short-circuitcurrent between the electrodes and the temperature in the seventhembodiment;

FIG. 19 is a sectional view of the electric power generating element ofthe eighth embodiment; and

FIG. 20 is a graph showing the relationship between the electromotiveforce and the temperature in the element of the eighth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

(1) Referring to FIG. 1, a positive electrode 1 and a negative electrode2 of the electric power generating element of the first embodiment areeach formed from a copper foil. A first or positive-electrodecomposition 3 is formed by heating 40 weight percentage of graphite("#90--300M", Nishimura Graphite) and 60 weight percentage ofpolyethylene glycol (Daiichi Kogyo Seiyaku Co., Ltd.) so that they aremelted and subsequently by impregnating a nonwoven fabric of polyesterresin with the melted material. The positive-electrode composition 3 isbrought into close contact with the positive electrode 1 in its meltedstate to be thereby secured to it.

A second or negative-electrode composition 4 is composed of 30 weightpercentage of lithium chloride ("Special-grade Reagent", Nakaraitesuku)and 70 weight percentage of polyethylene glycol. One side of thenegative-electrode composition 4 is secured to the negative electrode 2in the same manner as-in the positive-electrode composition 3 and asheet of kraft paper serving as a separator 5 is bonded to the oppositeside of the negative-electrode composition 4 such that the wholecomposition 4 is covered by the separator 5. The negative-electrodecomposition 4 covered by the separator 5 is pressed against thepositive-electrode composition 3 and the whole power generating elementis enclosed in a package (not shown) formed from a polyester film. Theelectric power generating element composed as described above has thewidth of 10 mm, the length of 65 mm and the thickness of about 1 mm.

FIG. 2 shows the relationship between an electromotive force and thetemperature when the above-described power generating element is heatedby means of a hot plate at the rate of about 0.45 deg/minute. In thiscase, a digital multimeter (Takeda TR 6841 and TR 6848) is used formeasurement of voltage and current and a digital thermometer (Takara D611) is used for measurement of the temperature. As obvious from FIG. 2,the electromotive force of about 0.6 V is generated at the roomtemperature or 20° C. and the electromotive force and the temperatureare gradually increased. The electromotive force of about 0.9 V isgenerated at about 120° C. On the other hand, FIG. 3 shows therelationship between a short-circuit current and the temperature. Asshown, the short-circuit current of the power generating element takesthe value of several ten milli amperes at the room temperature or 20° C.The short-circuit current is increased to about 20 mA at 110° C. Thus,it is understood that a large short-circuit current can be obtained forthe size of the power generating element and accordingly, it isconfirmed that a low-temperature heat energy is efficiently converted toan electric energy.

(2) The inventor made experiments with a liquid phase power generatingelement to explain the power generating mechanism of the element. Theliquid phase power generating element comprises a heat-transferablevessel or sampling bottle 30 formed from lath, as shown in FIGS. 4 and5. The sampling vessel 30 has the diameter of 35 mm and the height of 75mm. A solution 31 of 40 gram of lithium chloride and polyethylene glycolis contained in the sampling vessel 30. A copper electrode 32 having thewidth of 20 mm, the length of 65 mm and the thickness of 1 mm and agraphite electrode 33 having the same size as the copper electrode 32are fixed to a polycarbonate plate 34 with a gap of 5 mm between theelectrodes. The electrodes 32, 33 are hung on a silicon rubber plug 35in the sampling bottle 30. A part of each electrode immersed in thesolution 31 has the length of 37 mm. An agitator 36 is placed on thebottom of the sampling bottle 30 and a platinum temperature sensor (notshown) insulated by a polyethylene tube is inserted in the samplingbottle 30 from its top. The sampling bottle 30 is then placed on a hotstirrer 37. The agitator 36 is rotated by a rotating magnetic fieldproduced in the hot stirrer 37 so that agitated in the sampling bottle30, the solution is heated at the rate of 0.45 deg/minute by the hotstirrer 37. Thus, the relationship between the short-circuit current andthe temperature in the system of the lithium chloride having differentdensity is measured.

FIG. 6 shows the result of the above-described measurement. As obviousfrom FIG. 6, it is understood that the short-circuit current in thesystem of pure polyethylene glycol not containing lithium chloride issmall though it is shown by only two circles. The relationship betweenthe short-circuit current and the salt density is not so complicated andrather, it is understood that the short-circuit current depends upon thetemperature and the salt density. The reason for this is supposed thatthe short-circuit current depends upon the electrode reaction and aninner resistance.

(3) Influences of kinds of alkali chloride upon the element:

In the same manner as described above, the electromotive forces and theshort-circuit currents at various temperatures are measured in thesolutions of polyethylene glycol and each system of lithium chloride,sodium chloride and potassium chloride. FIGS. 7 and 8 show the resultsof the measurement. In this case, three kinds of salt take theapproximately same mol density. FIGS. 7 and 8 show that there is almostno difference in the electromotive force and the short-circuit currentamong the three systems of salt. This means that a role of each kind ofsalt is to provide each system with electrical conductivity and that anykind of salt can be employed if a desirable mol density can bemaintained.

(4) Relationship between the electromotive force and short-circuitcurrent and the temperature in the electric power generating element ofthe present invention:

As obvious from FIGS. 6 and 8, the short-circuit current has thetendency to be increased with increase of the temperature. On the otherhand, the electromotive force has the tendency to be decreased in thehigh temperature region, as obvious from FIG. 7. A more detailed studyof the results shows that the electromotive force has the tendency tovary in the high temperature region and also when the density of lithiumchloride is high. The reason for this is considered to be that aninterference reaction which will be described later occurs both when thetemperature is high and when the density of lithium chloride is high.This interference reaction in which the copper ions dissolve out fromthe negative electrode without the current flowing in the externalcircuit bears no relation to a discharge current flowing in the externalcircuit. In case that the interference reaction can be eliminated, thereis a possibility that the electromotive force and the short-circuitcurrent is sufficiently increased at the high temperature.

(5) Relation between the short-circuit current and the elapsed timeperiod and further analysis of the system:

The current changes were measured in the same manner as described abovein the case where the solution of 1 weight percentage of lithiumchloride and polyethylene glycol were maintained at a predeterminedtemperature (111° C., for example) and a short-circuit current wascaused to flow for a predetermined period of time. FIG. 9 shows theresult of the measurement. As obvious from FIG. 9, the current isdecreased to a large extent at an initial stage but subsequently, thedegree of decrease becomes small. For example, the inductively coupledplasma emission spectrometry shows that the polyethylene glycol solutioncontains 510 ppm of copper after one hour discharge. On the other hand,an amount of copper contained in an unused solution of polyethyleneglycol is below the analysis limit (>0.5 ppm). Accordingly, the value ofdissolved copper obtained from FIG. 9 is 48 ppm when the dissolvedcopper is univalent and 24 ppm when the dissolved copper is bivalent.

No difference can be found between the spectrum of the polyethyleneglycol solution after the discharge obtained by the infraredspectroscopic analysis and that of the unused polyethylene glycolsolution. However, the ultraviolet spectrum of the polyethylene glycolsolution after the discharge was measured by way of the spectrochemicalanalysis in ultraviolet and visible region and the result was comparedwith that of the unused polyethylene glycol solution. The sample of thepolyethylene glycol after the discharge shows a new large peak of 366nanometer in the shorter wavelength region and a new small peak of 426nanometer in the longer wavelength region. Further study needs to becarried out as to whether these peaks relate to an electrochemicalreaction or not, whether or not these peaks result from the thermaldecomposition having no relation to the electrochemical reaction, andwhether or not the dissolved copper ions result from absorption ofproducts from polyethylene glycol.

Dissolved copper ions will now be described. The density of copper is 24ppm as described above in case that the divalent copper dissolves out inthe result of measurement shown in FIG. 9, but this value is only onetwentieth of an actually measured value of 510 ppm. Consequently, it isconsidered that the mechanism that the copper ions dissolve out of thenegative electrode (a kind of interruption reaction) is concurrentwithout the current flowing in the external circuit. This property mayhave some relation to reduction in the electromotive power with theincrease in the density of lithium chloride as shown in FIG. 2. In casethat the above-mentioned interruption reaction actually occurs, animprovement over the interruption reaction will provide an improvementof the performance of the electric power generating element.

Second Embodiment

The construction of the electric power generating element of a secondembodiment will be described with reference to FIG. 10 which illustratesthe construction common to second through fifth embodiments. Thepositive electrode 6 of the power generating element is formed of thecopper foil. The positive-electrode composition 7 contains 10 weightpercentage of manganese dioxide serving as an activator, 40 weightpercentage of graphite ("#90--300M", Nishimura Graphite), and 50 weightpercentage of polyethylene glycol.

The negative-electrode composition 8 contains 28 weight percentage oflithium chloride ("Special-grade Reagent", Nakaraitesuku), 12 weightpercentage of zinc dust, and 60 weight percentage of polyethyleneglycol. The negative electrode 9 is formed by rolling a small quantityof lithium with an agate mortar (not shown) in the atmosphere ofnitrogen and pressing the rolled lithium on an aluminum foil. In thiscase, in consideration of a reaction of the negative-electrodecomposition 8 against liquid, it can be considered that only a part ofthe lithium employed in the negative electrode 9 serves as a metal.

The positive and negative compositions 7, 8 are heated to be melted inthe same manner as in the first embodiment and two sheets of thenonwoven fabric of polyester resin are impregnated with the respectivecomposition solutions. In this state, the compositions 7, 8 are securedto the respective electrodes 6, 9 with the separator 10 interposedtherebetween.

FIG. 11 shows the relationships between the electromotive force and theshort-current density and the temperature. As obvious from FIG. 11, thesecond embodiment obtains the electromotive force of 3.1 V and theshort-circuit current of 16 mA/cm² both higher than those in the firstembodiment. The reason is that the negative electrode 7 is formed fromlithium having a high ionization tendency and aluminum.

Third Embodiment

In a third embodiment, the positive and negative electrodes 6, 9 areboth formed from the copper foil in the same manner as in the firstembodiment. The positive-electrode composition 7 contains 10 weightpercentage of manganese dioxide (activator), 40 weight percentage ofgraphite ("#90--300M", Nishimura Graphite) and 50 weight percentage ofpolyethylene glycol. On the other hand, the negative-electrodecomposition 8 contains 28 weight percentage of lithium chloride("Special-grade Reagent", Nakaraitesuku), 12 weight percentage of zincpowder and 60 weight percentage of polyethylene glycol. Thesepositive-electrode and negative-electrode compositions 7, 8 are combinedwith each other with the separator 10 interposed therebetween.

FIG. 12 shows the relationships between the electromotive force and theshort-current density and the temperature. As obvious from FIG. 12, theelectromotive force and the short-circuit current in the thirdembodiment are lower than in the second embodiment but higher than inthe first embodiment. The reason for this is that manganese dioxideserving as the reagent facilitates the electrode reaction.

Fourth Embodiment

In a fourth embodiment, the positive and negative electrodes 6, 9 areboth formed from the copper foil in the same manner as in the first andthird embodiments. The positive-electrode composition 7 contains 10weight percentage of manganese dioxide (activator), 40 weight percentageof graphite ("#90--300M", Nishimura Graphite) and 50 weight percentageof polyethylene glycol. On the other hand, the negative-electrodecomposition 8 contains 28 weight percentage of lithium chloride("Special-grade Reagent, Nakaraitesuku"), 12 weight percentage ofmagnesium powder and 60 weight percentage of polyethylene glycol. Thesepositive-electrode and positive-electrode compositions 7, 8 are combinedwith each other in the same manner as in the second and thirdembodiments with the separator 10 interposed therebetween.

FIG. 13 shows the relationships between the electromotive force and theshort-current density and the temperature. As obvious from FIG. 13, theelectromotive force and the short-circuit current in the fourthembodiment are lower than in the second embodiment but higher than inthe first embodiment.

Fifth Embodiment

In a fifth embodiment, the positive and negative electrodes 6, 9 areboth formed from the copper foil in the same manner as in the first,third and fourth embodiments. The positive-electrode composition 7contains 10 weight percentage of manganese dioxide (activator), 40weight percentage of graphite ("#90--300M", Nishimura Graphite) and 50weight percentage of polyethylene glycol. On the other hand, thenegative-electrode composition 8 contains 28 weight percentage oflithium chloride ("Special-grade Reagent, Nakaraitesuku)", 12 weightpercentage of aluminum powder and 60 weight percentage of polyethyleneglycol. These positive-electrode and positive-electrode compositions 7,8 are combined with each other in the same manner as in the second,third and fourth embodiments with the separator 10 interposedtherebetween.

FIG. 14 shows the relationships between the electromotive force and theshort-circuit current density and the temperature. As obvious from FIG.13, the electromotive force and the short-circuit current in the fifthembodiment are lower than in the second embodiment but higher than inthe first embodiment.

Sixth Embodiment

The negative composition 8 contains sodium thiosulfate (Na₂ S₂ O₃)instead of lithium chloride. Sodium thiosulfate provides polyethyleneglycol with the ionic conductivity. the other composition is the same asthat in the first embodiment. FIG. 15 shows the relationship between theelectromotive force and the temperature and FIG. 16 shows therelationship between the short-circuit current and the temperature inthe sixth embodiment. Sodium thiosulfate is a reducing agent but anoxidizing agent is not present at the positive electrode side, so that ageneral battery is not constructed in the sixth embodiment. In thisembodiment, the increase in the electromotive force with increase of thetemperature is small up to 80° C. but becomes steep approximately at 90°C.

Seventh Embodiment:

The positive-electrode composition 7 contains 10 weight percentage ofmanganese dioxide (MnO₂) and 10 weight percentage of silver chloride(AgCl) as the activators. The other composition of the electric powergenerating element is the same as that in the first embodiment. FIG. 17shows the relationship between the electromotive force and thetemperature and FIG. 18 shows the relationship between the short-circuitcurrent and the temperature in the seventh embodiment. The electromotiveforce takes an approximately fixed value of 1 V in the range of 20° C.or above while the short-circuit current is steeply increased at about100° C.

Eighth Embodiment

In an eighth embodiment, the positive-electrode composition 11 is formedby melting 70 weight percentage of polyethylene glycol (Daiichi KogyoSeiyaku Co., Ltd.) by way of heating and mixing the melted polyethyleneglycol with 30 weight percentage of graphite (flake graphite or"#90--300M", Nishimura Graphite) with graphite being agitated. Thenegative-electrode composition 12 is formed by melting 70 weightpercentage of paraffin wax ("Microcrystalline wax Hi-Mic-2095", NipponSeirousha) and mixing the melted paraffin wax with 30 weight percentageof graphite (flake graphite or "#90--300M", Nishimura Graphite) with thegraphite being agitated.

The electric power generating element of the eighth embodiment hasenvelopes 13 and 14 formed from 50 μm of polyester film. Copperelectrodes 15 and 16 are bonded to the envelopes 13, 14 respectively.The melted positive-electrode and negative-electrode compositions 11 and12 are poured onto the copper electrodes 15, 16 respectively to behardened. Subsequently, the positive-electrode and negative-electrodecompositions 11, 12 are superposed upon each other. Lead wires 17 and 18are soldered to the electrodes 15, 16 respectively. FIG. 20 shows theelectromotive force obtained from the above-described electric powergenerating element.

In accordance with the present invention, the low-temperature thermalenergy can be efficiently converted to the electric energy as comparedwith the thermoelectric power generating element by use of the Seebeckeffect. Differing from the solar battery, the electric power generatingelement of this invention can provide the electric power when and wherelight is not available. Consequently, the low-temperature thermal energysuch as the exhaust heat, solar energy, ground heat or spa heat can beefficiently employed as the heat source. Thus, the present inventionprovides an economic power generation from which a sufficient energysaving can be achieved and which can also contributes to the globalenvironment protection. Furthermore, the raw material cost is low in theelectric power generating element of the invention. Consequently, theelectric power generating element of the present invention provides alarge cost reduction as compared with the thermoelectric powergenerating element or the solar battery. Additionally, the electricpower generating element of the invention provides a high-level safetyfor the human bodies as compared with the conventional chemical batterysince the compositions employed in the element of the present inventionare organic compounds non-noxious to the human bodies.

For the purpose of further increasing the energy converting efficiency,first, an activating agent may be added to the positive-electrodecomposition so that the electrode reaction is facilitated for increasein the electromotive force. Second, the negative electrode may be formedfrom a metal having a high ionization tendency for increase in theelectromotive force. Third, the nonwoven fabric may be impregnated witheach of the electrode compositions so that the thickness of the electricpower generating element is reduced for reduction in the internalresistance with the result of increase in the short-circuit current.

In the foregoing embodiments, the class of salt providing thepositive-electrode or negative-electrode composition with the ionicconductivity is not limited to the metallic halogenide (LiCl or NaCl).Instead, the metallic halogenide may be replaced with the inorganic acidmetallic salts such as Na₂ SO₄, K₃ PO₄ or NaNO₃, perchloric acidmetallic salts such as LiClO₄ or NaClO₄, the class of organic acid saltssuch as oxalate, formate or carboxylic acid salt.

The positive-electrode composition may contain carbon black instead ofgraphite. Furthermore, instead of the craft paper, the separator maycomprise parchment paper or various types of ionic conductive films.When each of these separators is interposed between the positive andnegative electrodes, the electrodes can be prevented from being broughtinto contact with each other even if the electric power generatingelement is thinned. However, means other than the separator may beemployed for preventing the electrodes from being brought into contactwith each other.

Furthermore, the nonwoven fabric impregnated with the positive-electrodeand negative-electrode compositions should not be limited to theabove-described one formed from the polyester resin. It may be replacedwith any one of other polyester resins, for example polypropylene fiber,which prevents the composition solution from permeating to the fiberinside. In the case of nonwoven fabric formed from natural fiber whichallows the composition solution to permeate to the fiber inside,polyethylene glycol and the carbon particles do not permeate at the samerate and consequently, the density of the components of the compositionbecomes nonuniform.

Although polyethylene glycol is employed as a main material of each ofthe positive-electrode and negative-electrode compositions in theforegoing embodiments, polyethylene glycol may be contained in eithercomposition. However, the positive-electrode composition needs tocontain graphite or graphite composition.

Although copper is employed as a metal composing the negative electrodein the foregoing embodiments, a metal having the ionization tendency aslarge as or larger than copper or its composition may be employedinstead.

The foregoing disclosure and drawings are merely illustrative of theprinciples of the present invention and are not to be interpreted in alimiting sense. The only limitation is to be determined from the scopeof the appended claims.

I claim:
 1. An electric power generating element converting heat energyto an electric energy, comprising:a) a positive electrode; b) a negativeelectrode formed from a metal; c) a positive electrode compositionprovided on the surface of the positive electrode and comprisingpolyethylene glycol and graphite particles dispersed in the polyethyleneglycol; and d) a negative electrode composition provided at a side ofthe negative electrode and comprising polyethylene glycol containing asalt providing an ionic conductivity.
 2. An electric power generatingelement according to claim 1, which further comprises fluid permeablecores impregnated with the positive electrode and negative electrodecompositions respectively, each core being formed of a nonwoven fabric.3. An electric power generating element according to claim 1, whichfurther comprises a separator interposed between the positive electrodeand negative electrode compositions.
 4. An electric power generatingelement according to claim 1, wherein the positive electrode compositioncontains an activator which is manganese dioxide.
 5. An electric powergenerating element according to claim 1, wherein the metal includingwithin its composition a metal having an ionization tendency as large asor larger than copper.
 6. An electric power generating element accordingto claim 1, wherein the negative electrode composition contains a metalpowder.
 7. An electric power generating element converting a heat energyto an electric energy, comprising:a) a positive electrode formed fromgraphite; b) a negative electrode formed from a metal; c) a solution ofpolyethylene glycol immersing both positive and negative electrodes; d)a salt contained in the solution of polyethylene glycol for providingthe same with an ionic conductivity; e) a heat-transferable vesselfilled with the solution of polyethylene glycol and transferring anexternal heat to the solution of polyethylene glycol; f) a siliconerubber plug insertable into the top of said heat transferable vessel;and g) a polycarbonate plate attached to said silicone rubber plug forsuspending said immersed electrodes.